A five layer sandwich
Thermal blinds are a great, low-cost, way of reducing heat loss through your windows. This could be especially useful if you’ve got an older property with single-glazed windows.
The blinds we’ve used for our Green Gables Dolls House are made up of five layers of material:
1. Room side fabric – 100% polyester with blackout surface (we’ve used velvet, but there are various colour options available from the Thermal Blind Co )
2. 12mic Aluminised Mylar – space blanket material originally developed by NASA
3. 7mm Thinsulate – a highly insulating thermal fleece, normally used for clothing (‘Clo’ value of circa 1.1)
4. 12mic Aluminised Mylar
5. Outside – 110g poly cotton blackout lining fabric
What difference do they make?
In December 2010 a six hour test of the the performance of this kind of blind was undertaken using a prototype fitted to a typical single-glazed Victorian window. The results showed that the blinds prevent a significant heat loss through the window glass and reduced downdrafts close to the window. The blind reduced the U-value of the window from 4.8W/sq.m/K (typical single glazed window value) to around 1.8 – 2.0 W/sq.m/K. This is equivalent to triple glazing.
OK, so what a U-value?
Thermal transmittance, also known as U-value, is the rate of transfer of heat through a structure (which can be a single material or a composite), divided by the difference in temperature across that structure. The units of measurement are W/m²K. The better-insulated a structure is, the lower the U-value will be. Workmanship and installation standards can strongly affect the thermal transmittance. If insulation is fitted poorly, with gaps and cold bridges, then the thermal transmittance can be considerably higher than desired. Thermal transmittance takes heat loss due to conduction, convection and radiation into account.
A U-value, is the reciprocal of an R-value.